In the Japanese legal system, a final and binding judgment (確定判決 - kakutei hanketsu) generally brings definitive closure to a dispute, with its contents protected by the principle of res judicata. However, a notable exception exists for judgments that order the payment of damages in periodic installments (定期金賠償 - teikikin baishō), such as those awarded for ongoing medical care, long-term nursing needs, or future lost income resulting from a tort like a personal injury. Recognizing that the future circumstances upon which such awards are based can change significantly over time, Article 117 of Japan's Code of Civil Procedure (CCP) provides a mechanism for parties to file a "lawsuit to modify a final judgment" (確定判決変更の訴え - kakutei hanketsu henkō no uttae). This article explores the nature of these modification lawsuits and, crucially, how the "value of suit" (訴額 - so'gaku) is determined for calculating court filing fees.

The Rationale for Modifying Judgments for Periodic Payments

Judgments ordering periodic payments are often predicated on assessments and predictions about future conditions. For example, an award for future medical expenses might be based on the plaintiff's prognosis at the time of the original trial, or compensation for lost future earnings might be calculated based on assumptions about life expectancy, career trajectory, and economic conditions.

If a "significant change in circumstances" (事情に著しい変更 - jijō no ichijirushii henkō) occurs after the original judgment becomes final—circumstances that were fundamental to the calculation of the periodic damage award—strict adherence to the original payment schedule could become unjust[cite: 87]. Such changes might include:

• An unexpected and significant improvement or worsening of the plaintiff's medical condition.
• Substantial changes in the cost of necessary care or treatment.
• Other unforeseen events that fundamentally alter the basis of the original award.

CCP Article 117(1) allows either party (the recipient or the payer of the periodic payments) to petition the court to increase or decrease the amount of future installments to reflect these new realities[cite: 87].

Legal Nature of the Modification Lawsuit

A lawsuit to modify a final judgment for periodic payments is characterized as a "formative lawsuit of a procedural nature" (訴訟法上の形成の訴え - soshōhōjō no keisei no uttae)[cite: 87]. Its primary legal effect is to:

• Extinguish the enforceability of the relevant part of the original judgment concerning future payments.
• Limit the res judicata effect of the original judgment with respect to those future payments, thereby paving the way for a new judicial determination.

If an increase in payments is sought and granted, the new judgment will also function as a judgment for performance, ordering the revised future periodic payments[cite: 87]. The judgment is essentially formative in that it reshapes the existing legal obligation established by the prior final judgment.

The "object of litigation" (訴訟物 - soshōbutsu) in a modification suit under CCP Art. 117 is considered to be the same as the original suit concerning the periodic payments, but it is specifically focused on the impact of the changed circumstances on those payments[cite: 87]. The assertion of a "significant change in circumstances" is not merely the introduction of new facts to support a new claim; it is an argument that challenges the continued appropriateness of the prior judgment's determination for the future, making this type of suit somewhat analogous to a retrial (再審の訴え - saishin no uttae) for this specific aspect of the judgment[cite: 87]. The parties to such a suit are the original parties to the judgment or their legal successors who are bound by it[cite: 87].

Key Requirements and Procedural Aspects

To successfully bring a lawsuit to modify a judgment for periodic payments:

• There must be a final and binding judgment that orders periodic payments for damages.
• A "significant change in circumstances" that were fundamental to the original calculation of the damage award must have occurred. Crucially, this change must have arisen after the conclusion of oral arguments in the original proceedings that led to the judgment being modified.
• The suit must be filed by an original party to the judgment or their legal successor[cite: 87].

Jurisdiction and Pleadings:

• Exclusive Jurisdiction: Lawsuits under CCP Art. 117 fall under the exclusive jurisdiction of the court of first instance that rendered the original judgment ordering the periodic payments (CCP Art. 117(2))[cite: 89]. This ensures that the court most familiar with the original basis of the award handles its potential modification.
• Pleadings: The plaintiff in the modification suit must clearly specify in their complaint the desired change to the operative part of the original judgment[cite: 88]. For example:
  • For an increase: "It is requested that Paragraph X of the judgment rendered by this court on [Date] in Case No. YYYY(Wa)ZZZ, concerning periodic payments due from [date of filing the modification suit] onwards, be modified as follows: The Defendant shall pay the Plaintiff the sum of ¥XXX per month."
  • For a decrease: "It is requested that the portion of Paragraph X of the judgment...ordering payments exceeding ¥YYY per month from [date] onwards be cancelled."
    A copy of the original final judgment must be attached to the complaint (Rules of Civil Procedure, Art. 49)[cite: 88].

Court's Decision:

• If the court finds that no "significant change in circumstances" has occurred or been proven, the modification suit will be dismissed. Such a dismissal has res judicata effect concerning the absence of grounds for modification as of that time. A party wishing to file another modification suit later would need to demonstrate a new and subsequent significant change in circumstances[cite: 88].
• If the court finds that a significant change justifying modification has been proven, it will issue a new judgment that alters the amount of the periodic payments prospectively, typically with effect from the date the modification suit was filed, or another date deemed appropriate by the court[cite: 88].
• Provisional execution (仮執行 - kari-shikkō) can be granted on a judgment ordering an increase in payments. The source material suggests that, based on principles of procedural fairness and symmetry, provisional execution should also be grantable for a judgment ordering a decrease, to allow the paying party to halt or reduce execution based on the (now excessive) original judgment amount[cite: 88]. Parties can also seek a stay of execution of the original judgment while the modification suit is pending (CCP Art. 403(1)(vi)).

Calculating the "Value of Suit" (So'gaku) for Court Fees

Given the exclusive jurisdiction rule, the calculation of jurisdictional so'gaku is not a primary concern for these modification suits[cite: 89]. The focus is on the "court fee so'gaku" (手数料訴額 - tesūryō so'gaku).

The general principle for calculating the so'gaku in a CCP Art. 117 lawsuit is that it represents the total monetary amount of the increase or decrease in periodic payments that the plaintiff is seeking for a specific, defined period[cite: 89].

Determining the "Specific Period" for So'gaku Calculation:

• While this period could theoretically be defined as the duration from the filing of the modification suit until the conclusion of oral arguments in that suit, such an approach would lead to uncertainty in fee calculation at the outset.
• Therefore, for normative reasons and to ensure predictability, the source material indicates that this period is typically considered to be one year[cite: 89].

Calculation Example (from the source text):
Assume an original final judgment ordered the Defendant to pay the Plaintiff periodic damages of ¥150,000 per month.

• If the Plaintiff files a modification suit seeking an increase to ¥200,000 per month:
  • The monthly difference (increase) sought is ¥50,000 (¥200,000 - ¥150,000).
  • The so'gaku for court fee purposes = ¥50,000/month × 12 months = ¥600,000[cite: 89].
• If the Defendant files a modification suit seeking a decrease to ¥100,000 per month:
  • The monthly difference (decrease) sought is ¥50,000 (¥150,000 - ¥100,000).
  • The so'gaku for court fee purposes = ¥50,000/month × 12 months = ¥600,000[cite: 89].

This "one-year difference" rule provides a practical and relatively standardized method for assessing the value of suit, and thus the initial court fees, for these specialized formative lawsuits that seek to adjust future obligations.

Conclusion

The lawsuit to modify a final judgment for periodic payments under Article 117 of the CCP is an important, albeit exceptional, tool in Japanese civil procedure. It allows for the adjustment of long-term damage awards to reflect significant, unforeseen changes in the underlying circumstances that were foundational to the original calculation. While the jurisdiction for such suits is fixed with the court that rendered the initial judgment, the court fees are determined by a "value of suit" that quantifies the total financial impact of the sought-after modification over a standardized one-year period. This approach balances the need for judicial flexibility in long-term awards with a predictable framework for the costs associated with seeking such modifications.